In recent years, portable gadgets such as audio devices and mobile phones are used in various fields, and as power sources therefor, primary batteries such as alkaline batteries and secondary batteries such as nickel hydride batteries and lithium-ion batteries are widely used. These batteries are required to have high performance such as high output and long life, and battery cases, in which electric generating elements such as positive electrode active materials and negative electrode active materials are accommodated, are also required to be improved in their performance as important constitutional elements of batteries.
In addition, application of a conductive film to the inner surface of a battery case is recently omitted in order to reduce volatile organic solvent, and hence, as the material for such a battery case, a material is desired which can maintain battery properties at a high level even without formation of any conductive film. For example, Patent Document 1 discloses, as such a material for battery cases, a material for battery cases which is configured such that nickel alloy plated layers are formed on both surfaces of a steel sheet, and the hardness of the plated layer to be the inner surface of a battery case is set at a higher value than that of the plated layer to be the outer surface of the battery case. According to the technique disclosed in Patent Document 1, however, the advantageous effect of enhancing the battery properties, in particular the advantageous effect of reducing the internal resistance, is not necessarily sufficient when any conductive film is not formed, and further improvement is thus desired.